1. Field of the Invention
The present invention relates to methods and apparatuses for crystallizing molecules and, more particularly, to methods and apparatuses for automating the crystallization of molecules, particularly macromolecules such as proteins.
2. Description of Related Art
Fast progress in the area of genomics has provided explosively growing databases of information on genes of human and other organisms by mapping, sequencing and analyzing their genomes. Many genes that may be critical for identifying people predisposed to certain diseases such as cancer have been discovered and their biological functions have been assessed in vitro and/or in vivo. Recently, a new area of genomics, functional genomics, has been developed, which involves a genome wide analysis of gene function by using information and reagents from the genomic analysis and expressing the genes in various organisms such as yeast. Functional genomics has generated important information regarding the expression pattern of genes by using high throughput screening techniques such as DNA oligonucleotide chips for specific genes or high density microarrays. An understanding of the network of interactions between a protein expressed by a target gene and other macromolecules in the cell is also being expanded at an unprecedented rate by using efficient screening methods such as the yeast hybrid systems.
One of the ultimate goals of these genome projects is the development of efficacious therapeutics against proteins expressed by disease genes. Among various methods of drug discovery and development, structure-based drug development has become one of the most important approaches, thanks to rapidly advancing computation techniques. It is well recognized that understanding of the detailed three-dimensional structure of a protein not only assists in rational drug design and development in the laboratory but also provides a well-defined target in high throughput drug screening by using computer-aided docking analysis.
Solving high resolution structures of protein in a high throughput fashion presents a major bottleneck in such a chain of genomics and drug development. High resolution structures of proteins are solved by X-ray crystallography, and more recently by using multi-dimensional NMR spectroscopy on high-field NMR machines for smaller proteins or peptides.
Various methods for X-ray crystallography have been developed, including the free interface diffusion method (Salemme, F. R. (1972) Arch. Biochem. Biophys. 151:533–539), vapor diffusion in the hanging or sitting drop method (McPherson, A. (1982) Preparation and Analysis of Protein Crystals, John Wiley and Son, New York, pp 82–127), and liquid dialysis (Bailey, K. (1940) Nature 145:934–935).
Presently, the hanging drop method is the most commonly used method for growing macromolecular crystals from solution, especially for protein crystals. Generally, a droplet containing a protein solution is spotted on a cover slip and suspended in a sealed chamber which contains a reservoir with a higher concentration of precipitating agent. Over time, the solution in the droplet equilibrates with the reservoir by diffusing water vapor from the droplet, thereby slowly increasing the concentration of the protein and precipitating agent within the droplet, which in turn results in precipitation or crystallization of the protein.
The process of growing crystals with high diffraction quality is time-consuming and involves trial-and-error experimentations on multiple solution variables such as pH, temperature, ionic strength, and specific concentrations of salts, organic additives, and detergents. In addition, the amount of highly purified protein is usually limited, multi-dimensional trials on these solution conditions is unrealistic, labor-intensive and costly.
A few automated crystallization systems have been developed based on the hanging drop methods, for example Cox, M. J. and Weber, P. C. (1987) J. Appl. Cryst. 20:366; and Ward, K. B. et al. (1988) J. Crystal Growth 90:325–339. A need exists for improved automated crystallization systems for proteins and other macromolecules.